[Android] Migrate user directories after update (#6287)
[Android] Migrate user directories after update (#6287)

I've played a bit with #6275, to make the iterator available for non-power users too.

this PR automate user data migration (which happens once per update). If the folder `koreader/scripts.afterupdate` contains a file `migrate` then files will be copied to internal dir preserving their relative path. Thus user data **needs** to have the same hierarchy as internal directories.

Shell scripts will be find and run if the folder `koreader/scripts.afterupdate` exists and has no `migrate file`.

In the case of `koreader/scripts.always` there's no migration available, just shell scripts.

Digging a bit seems not possible to create new directories on app internal storage (it just crashes on the emulator since API25). So very fancy extensions are not supported, but it is ok to override files and create new files if dir already exists.

Tested with:

```find scripts.afterupdate/                                            
scripts.afterupdate/
scripts.afterupdate/data
scripts.afterupdate/data/hyph
scripts.afterupdate/data/hyph/Roman.pattern
scripts.afterupdate/data/example.css
scripts.afterupdate/migrate
```

Results:

```
06-20 16:16:33.590  3584  3597 I KOReader: after-update: running migration
06-20 16:16:33.596  3584  3597 I KOReader: command cp /storage/emulated/0/koreader/scripts.afterupdate/data/hyph/Roman.pattern /data/user/0/org.koreader.launcher/files/data/hyph/Roman.pattern returned 0
06-20 16:16:33.600  3584  3597 I KOReader: command cp /storage/emulated/0/koreader/scripts.afterupdate/data/example.css /data/user/0/org.koreader.launcher/files/data/example.css returned 0
06-20 16:16:33.604  3584  3597 I KOReader: command rm /data/user/0/org.koreader.launcher/files/afterupdate.marker returned 0
```
Frenzie/koreader,poire-z/koreader,Markismus/koreader,Hzj-jie/koreader,Frenzie/koreader,koreader/koreader,koreader/koreader,NiLuJe/koreader,NiLuJe/koreader,mwoz123/koreader,pazos/koreader,poire-z/koreader